An engine may include one or more knock sensors to sense engine knock. In a petrol engine, knock occurs in an engine after an air-fuel mixture in the cylinder is ignited by a spark. In particular, the air-fuel mixture is ignited at a location in the cylinder outside of a flame front in the cylinder created by the spark. The second ignition after the spark ignition is produced by rising pressure in the cylinder and it causes a pressure oscillation in the cylinder that produces a ping or knocking sound in the engine. The engine block may include several cylinders and support structures that may improve or degrade the capacity of the engine knock sensors to detect engine knock. Consequently, two or more knock sensors may be deployed in an engine to detect engine knock. However, it may be difficult to detect engine knock with even two engine knock sensors since combustion noise and vibration of the engine block may mask engine knock that is detectable via the engine knock sensors.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: operating the engine with a first group of combusting cylinders in response to a first condition; operating the engine with a second group of combusting cylinders in response to a second condition; adjusting spark timing of a cylinder in response to an indication of knock via a first group of sensors during the first condition; and adjusting spark timing of the cylinder in response to an indication of knock via a second group of sensors during the second condition.
By adjusting spark timing in response to different groups of knock sensors during different engine operating conditions, it may be possible to provide the technical result of improved engine knock detection. For example, if all engine cylinders are active and combusting air and fuel, it may be desirable to assess the presence or absence of engine knock via two engine knock sensors. However, if one or more cylinders is deactivated and not combusting air and fuel, it may be desirable to assess the presence or absence of engine knock via a single sensor and ignore output of a second sensor. Deactivating one or more engine cylinders may reduce combustion noise and improve a signal to noise ratio of a knock sensor.
The present description may provide several advantages. In particular, the approach may improve engine knock sensing. Additionally, the approach may reduce the possibility of engine degradation. Further, the approach may improve engine knock sensing when cylinders of an engine are deactivated in different ways.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.